Triple-chamber cardiac pacemakers of that kind are known, for example, from U.S. Pat. Nos. 5,514,161 and 5,584,867. These patents provide structures with which it is possible to prevent conduction of an atrial tachycardia to the ventricle of a heart by means of the cardiac pacemaker.
Many of the per se known dual- and triple-chamber cardiac pacemakers are so-called demand cardiac pacemakers which are so designed that stimulation pulses to a chamber of a heart are triggered only if no natural heart action is detected within a predetermined time window. In connection with ventricular cardiac pacemakers for example reference is made to a ventricular escape interval or an AV-time which is triggered with a stimulation or a natural event in the right atrium of the heart and at the end of which a ventricular stimulation pulse is produced if that is not inhibited because, during the ventricular escape interval, an event was detected in the heart ventricle to be stimulated.
Such a detected event (V-sense) can be caused by a natural contraction of the ventricle. Similar electrical signals as occur upon the natural contraction of a ventricle can however also be produced by crosstalk of signals produced in the atrium of a heart, for example an atrial stimulation, to the ventricle. In order to blank out the detection of such signals originating from the atrium in the ventricle pacemakers usually have a blanking time which is triggered for example with the application of a stimulation pulse to the right atrium of a heart and lasts for example 100 ms. During that blanking time no ventricular sense events are detected so that potentials which possibly occur in that blanking time in the ventricle do not result in inhibition of the delivery of a ventricular stimulation pulse.
In general terms there is a wish for the blanking time to be selected to be as short as possible in order more specifically to prevent crosstalk of atrial stimulation pulses into the sensing channel for ventricular events, but at the same time to detect natural ventricular events, in particular premature ventricular contractions (PVC). Detecting and taking account of such premature ventricular contractions is also desirable for the reason that they can suppress the delivery of a ventricular stimulation pulse. Otherwise, in the worst case scenario, a ventricular stimulation pulse could be triggered in such a way that it occurs in the so-called vulnerable phase after a ventricular contraction.
The above-outlined problems are countered in various different ways in dual-chamber cardiac pacemakers. Reference may be made here to U.S. Pat. Nos. 5,776,167 and 4,825,870. The cardiac pacemaker in accordance with U.S. Pat. No. 4,825,870 counters the above-outlined problems by the provision of a variable blanking time and a subsequent crosstalk window, during which ventricular events are detected and identified as crosstalk events.
The state of the art does not indicate hitherto that, in the case of a triple-chamber cardiac pacemaker, crosstalk on the basis of atrial stimulation can be attributed not only to stimulation of the right atrium (as is known in the case of dual-chamber cardiac pacemakers) but stimulation of the left atrium. The invention already starts with the realisation that stimulation of the left atrium occurs in respect of time after stimulation of the right atrium, more specifically after an atrial conduction time, so that crosstalk from the left atrium to the (right) ventricle can only occur markedly after the crosstalk of a right-atrial stimulation pulse.